The invention relates to a method and to a device for identifying foreign bodies in a base textile material, wherein the base textile material is subjected to radiation, and the radiation reflected on the base material is detected and converted into an electrical signal.
Base textile material is here taken to mean, for example, a fibre composite made of textile fibres such as a strip, a roving yarn, a yarn made, for example, of cotton or polyester fibres or mixtures thereof, etc. or a composite made of a fibre composite of this type such as a nonwoven, a woven, a knitted fabric, etc. A base textile material is taken to mean a base material which can contain foreign bodies but is predominant in terms of quantity. Such foreign bodies are, for example, foreign fibres in the fibre composite, portions of plastic films which, for example, are reduced in size to form narrow strips or fibres, vegetable matter (such as husk contents) of the cotton and other unwanted substances, such as hairs, feathers, etc. which can occur as plant components.
A method of this type and a device are known from WO 95/29396. Here, the base material, for example a yarn, is irradiated, with white light from one light source or alternately with light of various wavelengths i.e. for example yellow, green or red light from various light sources, against an absorbent background. The light reflected by the base material is detected by at least one receiver which detects the spectrally different portions of the radiation at different times. Therefore, a single receiver can alternately receive the various colours or an individual receiver can be provided for each colour, so all colours are simultaneously detected by different receivers. The receiver or receivers generate(s) a respective electrical signal corresponding to the preferably received wavelength of the radiation. These signals are then brought into a relation with one another, for example balanced with one another, in order to compensate for unwanted effects. Such an unwanted effect may, for example, be that the reflected light depends not only on the colour of the yarn and of the foreign body but also on the mass, volume or diameter of the yarn. The effect of the mass or the volume, for example, can be eliminated by said balancing, so, for example, only the effect of the colour of the yarn can be identified. A foreign body in the material can thus be reliably identified.